During the supporting period of this investigation different aspects of chromium-cobalt alloys, such as reaction of mold and investment, effect of manipulative variables on physical properties, and behavior of some recently developed alloys for use as dental prosthetic materials, were studied. Recently, the effect of addition of previously untried elements are being determined. Through the support of this study, two chromium-cobalt-base alloys were developed with improved physical properties. Both of the newly developed alloys are more ductile (elongation of 10% as compared to 2 to 3%), both are somewhat softer, and possess the same modulus of elasticity, when compared to other commercially available alloys. The second alloy has about 15% higher strength properties than the first alloy. Studies in the area of chromium-cobalt alloys as used in dentistry are being continued. Fatigue and corrosion properties of these alloys are being compared. A special home designed apparatus, one which closely simulates the behavior of partial denture clasps in practice, is being used to gauge the opening of partial denture clasps (cast and wrought, as well as those made of gold, Cr-Co, Cr-Ni and Cr-Fe alloys). The corrosion resistance properties of these alloys are compared to one another using a sensitive apparatus. The apparatus is a modified form of N.D. Greene and W.D. France's apparatus successfully used in industry. Techniques of electron microscopy, both electron and x-ray diffraction, electron probe microanalysis, and scanning microscopy are being used to identify the structure, morphology and interfacial relationships of various phases, and their effect on the properties. The ultimate aim of the study is to further increase the resistance of these alloys to corrosion, and possibly to further improve their mechanical properties to become more suitable for various biomechanical needs.